Adhesively bonded titanium structural components have been used in aircraft applications for many years. Service experience with these bonded structures has been varied with frequent failures from debonding of titanium articles. The bonding failures can be attributed to the different interfacial structures of the variously treated adherends. Numerous titanium surface treatments have been developed and used to promote adhesion and reduce the number of bonding failures. Among these are the method of anodizing titanium to promote adhesion disclosed in the U.S. Pat. No. 3,959,091, issued to Y. Moji and J. A. Marceau. Although the latter treatment significantly increases the bond performance of titanium articles, under certain conditions an apparent brittle oxide failure weakness still occurs near or at the metal oxide primer interface.
It is therefore an object of the present invention to eliminate this apparent brittle oxide failure weakness while maintaining the bonding strength of titanium articles at or equal to that achieved by the method disclosed in the aforementioned patent.